GENERAL I ARTICLE

Evolution to 3G Mobile Communication 2. Development towards Third Generation Systems

R Ramachandran

In the first partl of this article two examples of first genera­tion cellular systems, NMT and AMPS have been de­scribed. The features of2G, GSM, CDMA and the charac­teristics of first generation CDMA, IS-95 have also been discussed. In this part, the concepts of 2.5G and 3G stan­dards are presented.

1. Evolution of 2G Systems to 3G Systems

Customer demand for digital services is the major impetus for 3G. However, there is a huge technical jump from 2G to 3G.

New technologies and standards take years to develop and

deploy. A gradual evolution from 2G digital telephony GSM to

3G was envisioned by telephone carriers as the logical step, and

a set of extensions to GSM data services were designed and

standardized, giving rise to 2.S systems (HSCSD, GPRS, and EDGE). Researchers developed 2.S-generation technologies as

upgrades to 2G approaches. 2.SG has more bandwidth than 2G

but less than 3G. 2.SG uses ex'isting ?G spectra and does not

require an entirely new network infrast~ucture and thus can be implemented faster and less expensively than 3G. It essentially

'bridges' technologies that allow service providers a smooth

transition from 2G to 3G systems. Customers also can start receiving limited 3G features before 3G is fully available. The 2.SG approach includes high-speed circuit-switched data

(HSCSD) technology, a GSM extension that offers throughput

of up to 38.4 kbps [1].

2.SG systems use improved digital radio and packet-based tech­

nology with new modulation techniques to increase data rates, systems efficiency and overall performance. Their greatest ad­vantage is that despite changes they remain compatible with 2G

R Ramachandran is at Sri

Venkateswara College of

Engineering,

Sriperumbudur. His area

of interest includes

communication systems,

computer networks,

mobile computing and

neural networks.

1 Part 1. Second Generation Cel­

lular Systems, Resonance,

Vol.8, No.8, pp.62-72, Septem­

ber 2003 .

Keywords

Mobile networks, wireless com­

munication, third generation

systems.

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From a user's

standpoint, the

transition from 2G to

3G is transparent;

2G services are also

provided by 3G

services. However,

from the service

provider's viewpoint,

the migration to 3G

is difficult, risky and

costly.

Although the

number of different

data transmission

services in the

GSM is quite high,

their main

drawback is slow

data rate.

GENERAL I ARTICLE

systems. An added benefit is the low cost of the changes as

compared to moving to totally new 3G systems.

From a user's standpoint, the transition from 2G to 3G is

transparent; 2G services are also provided by 3G services. How­ever, from the service provider's viewpoint, the migration to 3G is difficult, risky and costly. Most 2G equip men t must be repla­ced to support 3G. 3G also requires a larger frequency spectrum, which is particularly scarce and costly. For this reason deploy­ing interim 2.SG systems makes sense. It provides significant improvements over 2G but does not require large investments.

1.1 CdmaOne, IS-95B (2.5G)

IS-9SB is the packet mode version of direct sequence CDMA standard IS-9SA technology. IS-9SB enhancements have been introduced to allow for high-speed data packet transmission. IS-9SB supports multiple codes per mobile station on both the

downlink and uplink. By combining CDMA code channels,

rates of 64 kbps are possible. These rates are significantly above the data rates provided by 2G systems. However they are not yet sufficient to be labeled 3G, which envisages speeds in excess of 144 kbps for mobile users and 2 Mbps for stationary users. The migration path from IS-9SA, a 2G technology, to IS-9SB is straightforward. Virtually all investments made by service pro­

viders remain viable. Some hardware modifications are required, but the greatest change is to the system software.

1.2. High-Speed Circuit-Switched Data (HSCSD-2.5G) in GSM

Although the number of different data transmission services in the GSM is quite high, their main . drawback is slow data rate.

The data rate is insufficient for most Internet applications and the connections can be very expensive due to their duration. Therefore a lot of effort has been made to improve data transmis­sion capabilities of the GSM system. Two solutions have been proposed:

________ LAA~AA, __ ------38 v V V V V v RESONANCE I November 2003

GENERAL I ARTICLE

• Increasing the data rate with the minimum system modi­fication - this is realized by the assignment of several time slots to a single connection.

• Better usage of the system resources by application of packet-switched communications with the possibility of assign­

ing several time slots in a frame for transmission of a data packet.

As a result, substantial modifications are required.

HSCSD is a feature that enables the simultaneous allocation of multiple full-rate traffic channels (TCH/F) of GSM to a user.

The aim of HSCSD is to provide a mixture of services with different air interface rates by a single physical layer structure. The available capacity of a HSCSD configuration is several

times the capacity of a TCH/F, leading to a significant enhance­

ment in the air interface data transfer capability. Ushering faster data rates into the mainstream is the new speed of 14.4 kbps per

time slot and HSCSD protocols that approach wire line ·access

rates of up to 57.6 kbps by using multiple 14.4 kbps time slots.

The increase from the current baseline 9.6 kbps to 14.4 kbps is

due to a nominal reduction in the error-correction overhead of

the GSM radio link protocol (RLP), allowing the use of a higher

data rate.

For end users, HSCSD enables the roll-out of mainstream high-. end segment services that enable faster Web browsing, file downloads, mobile video conference and navigation, telematics,

and bandwidth-secure mobile LAN access. Value added service providers (VASP) will,also be able to offer guaranteed quality of

service and cost efficient mass-market applications, such as

direct IP where users make circuit-switched data calls straight into a GSM network router connected to the Internet. To the

end user, the VASP or the operator is equivalent to an Internet

service provider (ISP) that offers a fast, secure dial-up service at cheaper mobile-to-mobile rates. HSCSD was the first inajor attempt to improve data transmission capabilities of the GSM system. Due to the assumption about introducing few changes

The aim of HSCSD

is to provide a

mixture of services

with different air

interface rates by a

single phYSical

layer structure.

For end users,

HSCSD enables the 1

roll-out of

mainstream high-end

segment services

that enable faster

Web browsing, file

downloads, mobile

video conference

and navigation,

telematics, and

bandwidth-secu re

mobile LAN access.

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GPRS is a major

improvement and

extension of the

standard GSM

system, which

takes into account

the increasing

demand for data

transmission over

mobile networks.

GENERAL I ARTICLE

in the system, the HSCSD remains a circuit-switched system, as

the standard GSM is. Therefore it is not well suited to the packet

traffic which is characteristic for data transmission. The reser­vation of more than one time slot during the whole data ex­

change session increases the probability of blocking in a cell.

One disadvantage is reduced network voice capacity, since it

removes channels from service that would normally be used to

support voice calls. Since the user requires more system re­sources, the cost of the connection can be significantly higher

than a normal voice call. Nevertheless, this enhancement does allow GSM systems to support higher data rates. HSCSD lessens

the financial impact of providing users with higher data rates

since it is primarily a software upgrade. Some hardware is

required in the form of gateway equipment to connect the system to data networks (e.g., the Internet). But this equipment

is minimal and easy to implement.

1.3. General Packet Radio Service (GPRS - 2.SG)

The next phase in the high speed road map is the evolution of

current short message services, such as smart messaging and

unstructured supplementary service data (USSD), toward the

new GPRS, a packet data service using TCP/IP and X.2S to offer

speeds up to 171 kbps [2]. This data rate is high enough to permit video conferencing and interacting with multimedia

Web sites. GPRS is a major improvement and extension of the standard GSM system, which takes into account the increasing

demand for data transmission oyer mobile networks. Data trans­

mission rates in the existing mobile networks were insufficient

and the connection set-up time was long. The circuit-switched

transmission was not well fitted to the bursty and asymmetric

nature of data traffic; therefore the existing system resources

were 'Used inefficiently. As a result, it was decided that packet­

switched transmission should be applied. Thus, system users can share the same physical channels and the system resources can be used much more efficiently due to statistical multiplex­ing.

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GENERAL I ARTICLE

GPRS has been standardized to optimally support a wide range of applications ranging from very frequent transmission of me­dium and large data volume to infrequent transmission of large

data volume. GPRS has been developed to reduce connection setup time and allow an optimum usage of radio resources. It provides a packet data service for GSM where time slots on the air interface are multiplexed to transmit packet data from sev­eral rnobile stations. The consequence of packet switching is a tariff system based on the number of transmitted packets. The session can last for a long time but the user pays for the transmit­ted data volume only. GPRS differs from HSCSD by achieving improved transfer speeds by dynamically assigning time slots on

GSM radio channels [1].

GPRS provides a core network platform for current GSM opera­

tors not only to expand the wireless data market in preparation for the introduction of 3G services, but also a platform on which

to build IMT-2000 frequencies should they acquire them. GPRS enhances GSM data services significantly by providing end-to­

end packet-switched data connections. This is particularly effi­

cient in Internet/intranet traffic, where short bursts of intense

data communications activity are interspersed with relatively long periods of inactivity. Because there is no real end-to-end

connection to be established, setting up a GPRS call is almost instantaneous and users can be continuously online. Because GPRS does not require any dedicated end-to-end connection, it

only uses network resources and bandwidth when data is actually being transmitted. This means that a given amount of radio

bandwidth can be shared efficiently and simultaneously among many users. Thus GPRS goals are to efficiently service data

sources and to provide a packet switched service that shares GSM resources. The physical layer (air interface) ofGPRS is the same as GSM. The challenge is maintaining compatibility with the circuit-switched GSM network and the packet-switched Internet

system. GPRS uses the same GSM modulation scheme, frames

and multiple-access method. The implementation GPRS has a

limited impact on the GSM core network. It simply requires the

The physical layer

(air interface) of

GPRS is the same

as GSM. The

challenge is

maintaining

compatibility with

the circuit-switched

GSM network and

the packet­

switched Internet

system.

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EDGE, developed

initially by Ericsson

and scheduled for

commercial use

this year, provides

an evolutionary

path that enables

existing 2G

systems (GSM, IS-

136) to deliver 3G

services in existing

spectrum bands.

GENERAL I ARTICLE

addition of new packet data switching and gateway nodes, and an

upgrade to existing nodes to provide a routing path for packet

data between the wireless terminal and a gateway node. The

gateway node provides interworking with external packet data

networks for access to Internet, intranets, and databases.

GPRS will support all widely used data communications proto­

cols, including IP, so it will be possible to.connect with any data

source from anywhere in the world using a GPRS mobile termi­nal. GPRS will support applications ranging from low speed

short messages to high-speed corporate LAN communications.

However, one of the key benefits of GPRS - that it is connected

through the existing GSM air ipterface modulation scheme - is

also a limitation, restricting its potential for delivering data

rates higher than lIS kbps. To build even higher rate data

capabilities into GSM, a new modulation scheme is needed.

1.4 Enhanced Data Rates for GSM Evolution (EDGE 2.SG)

EDGE, developed initially by Ericsson and scheduled for com­mercial use this year, provides an evolutionary path that enables

existing 2G systems (GSM, IS-136) to deliver 3G services in existing spectrum bands. Like GSM, it supports voice, but

provides significant data rate improvements. EDGE reuses the

GSM carrier bandwidth and time slot structure. The standard­ization effort for EDGE has two phases. In the first phase the

emphasis has been placed on enhanced GPRS (EGPRS) and enhanced CSD (ECSD). The second phase is being defined with

improvements for multimedia and real-time services as possible work items.

The EDGE air interface is designed to facilitate higher bit rates than those currently achievable in existing 2G systems. The

modulation scheme based on eight level phase shift keying (8-

PSK) is used to increase the gross bit rate. Using enhanced 8-

PSK modulation a three-fold data rate increase over standard two-level GMSK modulation is possible. Specifically, EDGE provides 69.2 kbps/slot throughput vs. 22.8 kbps/slot of a stan-

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GENERAL I ARTICLE

dard GSM carrier. Throughputs can be further increased to approximately 474 kbps by using multiple slots.

The improved data rates are not free. In the case of EDGE, 8-

PSK provides higher data rates at the cost of requiring higher

signal to noise ratios. This typically means higher RF power

requirements. A mobile terminal can save power by supporting 8PSK only when RF signal conditions are favorable. Another

consequence of 8 PSK modulation is the need for increased linearity of costly RF power amplifiers.

EDGE's major advantage is that by modifying the GSM air

interface slightly, EDGE modulation can be time inserted on a

slot-by-slot basis. This allows EDGE systems to coexit with GSM systems. First generation GSM cellular phones will ignore EDGE time slots since they cannot be demodulated or decoded.

The evolutionary path from GSM to EDGE has minimal impact

on the existing network architecture and the ability to reuse

installed equipment is a big advantage. Changes to support

EDGE are limited to the radio portion of the network (e.g., base

station); all other network interfaces remain largely·unchanged.

2. Third Generation (3G) Systems

Since existing systems operate in selected environments only, it

would be desirable to create a new universal system (3G system),

which could operate anywhere, anytime using unified equip­

ment. Also, taking into account the limitations imposed by the

finite amount of radio spectrum available, the focus of 3G

mo bile systems is an economy of network and radio transmis­sion design to provide seamless service from the customer per­spective. Third-generation systems are perceived as the wireless

extension Qf future fixed networks, as well as an integrated part of the fixed network infrastructure [3].

The research on third generation systems was initiated long

before the potential of the GSM .and other second-generation

systems were exhausted. The aim was to create a global standard, which would enable global roaming. The International Tele-

EDGE's major

advantage is that

by modifying the

GSM air interface

slightly, EDGE

modulation can be

time inserted on a

slot-by-slot basis.

This allows EDGE

systems to coexit

with GSM

systems.

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Multimedia and

video conferencing

are the services

that are expected

to justify the new

infrastucture.

3G is expected to

support international

roaming. Currently,

roaming between

international

networks requires a

different cellular

phone for each

network.

GENERAL I ARTICLE

communications Union (lTU) began to work on the third gen­eration mobile communication system by defining the basic

requirements. The system was initially called Future Public

Land Mobile Telecommunication System (FPLMTS) and now

is known as International mobile Telecommunications (IMT-

2000). Minimum IMT-2000 requirements include:

High-speed data transmissions: 3G will bring an order of magni­

tude improvement to data communications enabling bandwidth

hungry multimedia applications. Although the use of email and

web browsing is skyrocketing, they are not killer applications

that justify a high investment in 3G. Multimedia and video

conferencing are the services that are expected to justify the new

infrastucture. 3G data rates fall into three categories:

• 2 Mbps for indoors and for pedestrians. • 384 kbps for terminals moving at no more than

120 km/h in urban areas.

• 144 kbps in rural areas and for fast moving vehicles.

Symmetrical and asymmetrical data transmission support:

Email and web browsing is predominately asymmetrical. For example, data transmitted to the user is much greater than that

transmitted by the user. However, services such as video conferencing are symmetrical resulting in equal data transmis­

sion in both directions.

Improved voice quality: Provide voice quality comparable to that of wire-line telephony.

Greater capacity: With the explosion in usage, the need to

efficiently use the frequency spectrum is imperative.

Multiple simultaneous services: This allows, for example, a user

to download an MP3 audio file while talking on the same cell­

phone. Support of global mobility: 3G is expected to support interna­tional roaming. Currently, roaming between international net­works requires a different cellular phone fot each network.

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GENERAL I ARTICLE

Improved security: Users will be able to communicate and

conduct business in a secure environment. This will ultimately

foster additional commercial services.

Service flexibility: Both circuit-switched (e.g., voice, real-time

video) and packet-switched services (e.g., Internet Protocol) shall be supported.

Third generation (3G) wireless systems will offer access to

services anywhere from a single terminal; the old boundaries between telephony, information, and entertainment services

will disappear. Mobility will be built into many of the services currently considered as fixed, especially in such areas as high­

speed access to the Internet, entertainment, information, and

electronic commerce (e-commerce) services. The distinction

between the range of services offered via wireline or wireless will

become less and less clear and, as the evolution toward 3G

mo bile services speeds up, these distinctions will disappear

wi thin a decade.

Applications for 3G wireless networks will range from simple voice-only communications to simultaneous video, data, voice

and other multimedia applications. One of the main benefits of

3G is that it will allow a broad range of wireless services to be

provided efficiently to many users.

Packet-based Internet Protocol (IP) technology will be at the

core of the 3G services. Users will have continuous access to

online information. Email messages will arrive at hand-held

terminals nearly instantaneously and business users will be able

to stay permanently connected to company intranets. Wireless users will be able to make video conference calls to the office and

surf the Internet simultaneously, or play computer games inter­

actively with friends in other locations.

The 3G specifications required participation from companies

and agencies worldwide to assure that the standard is globally accepted. In 1998, the 3GPP (third generation partnership project) was established in order to define a common wideband

Third generation

(3G) wireless

systems will offer

access to services

anywhere from a

single terminal; the

old boundaries

between telephony,

information, and

entertainment

services will

disappear.

Packet-based

I nternet Protocol

(IP) technology will

be at the core of

the 3G services.

Users will have

continuous access

to online

information.

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GENERAL I ARTICLE

CDMA standard. As a result the Universal Mobile Telecommu­nications System (UMTS) was defined. However, those partners

who wished to extend the IS-95 system also promoted an alter­

native standard called CDMA2000. The 3GPP developed the UMTS Frequency Division Duplex (FDD) and UMTS Time Division Duplex (TDD) specifications with 5 MHz carrier spac­

ing. The 3GPP2 produced lxEVDO (IS-856) that is a part of the

larger CDMA2000 specification. Other technologies such as

Digital Enhanced Cordless Telecommunication (DECT +) also

come under the 3G umbrella. They also agreed upon the stan­

dards MC CDMA (Multicarrier CDMA) and UWC136 (Univer­sal Wireless Communications). UWC136 standard is based on

the convergence of IS136 and GSM EDGE. The UWC136 will be a natural extension ofTDMA systems. However, they are not

expected to be widely deployed due, in part, to the technical

superiority of other technologies, as well as non-technical busi­

ness and political issues. In fact three different IMT -2000 stan­

dards were agreed upon:

• UTRA (UMTS Terrestrial Radio Access) - wideband CDMA transmission with FDD and TDD modes and 5 MHz carrier

spacing,

• MC CDMA (Multicarrier CDMA),

• UWC136 (Universal Wireless Communications) - based on the convergence of IS-136 and GSM EDGE. The UWC136 will be a natural extension of TDMA systems.

2.1 UMTS (3G)

The basic purpose of introducing UMTS is to support inte­

grated digital wireless communications at data rates up to 2Mbps

in the 2 GHz band. Table 1 presents the bands allocated to the

UMTS.

The UMTS requirements are similar to those stated for IMT-2000 [4]. They are:

Operation in various types of environment: The terrestrial part

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GENERAL I ARTICLE

Frequency [MHz] Bandwidth [MHz] Destination

1900-1920 20 UMTS (terrestrial), TOO

1920-1980 60 UMTS (terrestrial) FOO, UL

1980-2010 30 UMTS (satellite) FOO, UL

2010-2025 15 UMTS (terrestrial) TOO

2045-2 I 10

2 I 10-2170 60 UMTS (terrestrial) FOO, OL

2170-2200 30 UMTS (satellite) FOO, OL

of the UMTS will operate in several environments, from rural to indoor. There will be three basic types of cells fitted to these

environments: picocells, microcells and macro cells with appro­priate physical layers of the UMTS.

The choice of duplex transmission: The bandwidth allocated

consists of two paired bands and two unpaired bands. Frequency

division duplex transmission is applied in the paired bands and

time division multiplex in unpaired bands.

A wide service offer: The UMTS should support a large selec­

tion of services, from voice transmission to fast data transmis­

sion. The traffic can be asymmetric. The system should be

flexible enough to allow for the introduction of new services in

the future.

Integration with fixed networks: The UMTS will be integrated

with wireline wideband networks such as B-ISDN.

Following the above requirements a list of services has been

proposed and their quality has been defined. Table 2 gives the

service proposals. The UMTS offers voice, data and video tele­phony transmission. Besides that, it can be treated as a wireless

extension of integrated services digital networks. Therefore the system supports basic ISDN access at the rate of 144 kbps (two B

channels plus a D channel). Data transmission at the rate of 2

Mbps, possible in a limited range, allows transmission of com­pressed video. Similar to the second-generation systems, the UMTS will ensure a high level of security of transmitted data. It

Table 1. UMTS spectrum

allocation.

The UMTS should

support a large

selection of

services, from

voice transmission

to fast data

transmission. The

traffic can be

asymmetric. The

system should be

flexible enough to

allow for the

introduction of new

services in the

future.

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GENERAL I ARTICLE

Type of Service Data Rate Error Rate Allowable Delay

[kbpsJ [msJ

Speech transmission 4.75-12.2 10-4 40

Voice band data 2.4-64 10-5 200

Hi-Fi sound 940 10-6 200

Videotelephony 64-144 10-7 40-90

Email 0-384 10-6 many minutes

Facsimile (G4) 64 10-6 100

Broadcast or multicast

Transmission 1.2-9.6 10-6 100

Short messages/paging 1.2-9.6 10-6 100

Web browsing 16-64 (UL) 10-6 seconds

96-384 (DL) 10-6

Access to database 2.4-768 10-6 200

Teleshopping 2.4-768 10-7 90

Electronic newspaper 2.4-2000 10-6 200

Navigation and location 64 10-6 100

Table 2. Examples of ser­

vices in UMTS.

UMTS is also

referred to as Wide

band COMA

(WCOMA).

WCOMAis now

recognized as one

of the leading

candidates for third

generation

wireless access.

is important not only for the privacy of individual telephone

calls, but also for the support of tele-banking and e-commerce.

UMTS applies a high quality Adaptive Multi-Rate (AMR) speech

coding based on Algebraic Code Exited Linear Prediction (ACELP) coding with discontinuous transmission and comfort noise insertion. It works at 8 different bit rates: 4.75,5.15,5.90,

6.70, 7.40, 7.95, 10.20, and 12.20 kbps. Three of them are com­patible with speech coders applied in the existing second-gen­

eration systems: 4.70 kbps PDC EFR, 7.40 kbps IS-641 (US

TDMNIS-136) and 12.20 kbps GSM EFR. The data rate of the AMR coder depends on the network load, the serv-ice level

specified by the network operator and the current SNR value.

UMTS is also referred to as Wide band CDMA (WCDMA).

WCDMA is now recognized as one of the leading candidates for

third generation wireless access. It gets its name from its 5 MHz wide bandwidth requirement and is based on direct-sequence

spread-spectrum with a chip rate of 3.84 Mcps. It will support

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GENERAL' I ARTICLE

circuit and packet data access at nominal rates up to 384 kbps in

macro cellular environments, and provide simultaneous voice

and data services. The large bandwidth of WCDMA stems from

the direct sequence chip rate of 3.84 Mcps. This is much larger

than the 1.2288 Mcps rate of Cd rna One and CDMA2000 IxRTT

(ltime Is-95 Radio Telephone Technology) that requires

1.25MHz, and the 3.6864 Mcps rate of CDMA2000 3x

multicarrier (3x MC). The chip rate is the primary difference

between the two technologies and a major reason for their incompatibility [3,4].

The transition from GSM to WCDMA requires a new frequency

spectrum because of the 5 MHz of bandwidth that the WCDMA

waveform requires. It cannot fit into the smaller spectrum space

currently allocated to GSM. This and other factors make the transition from GSM to WCDMA revolutionary. Besides the frequency spectrum required, the modulation method is very different. This makes the technologies incompatible and more

accurately labels WCDMA as a new design rather than an evolution or enhancement of GSM.

2.2. CDMA2000, IS-2000 (3G)

CDMA2000 is one of the most important proposals for an IMT-

2000 air interface. CDMA2000 is formally documented as IS-

2000 and builds on its predecessor CdmaOne (IS-95). It has

much in common with the 2G version of CDMA. It uses similar

modulation techniques and Walsh codes but enhancements give it greater flexibility and performance. One major improvement of CDMA2000 is its ability to support higher data rates. Peak

data rates of 153 kbps are possible with low-end phones, and

rates as high as 307 kbps are possible with high-end phones and devices. Additional changes to the IS-95 specification nearly doubles voice capacity and the addition of a 5ms frame supports 'quick paging' which improves battery life. CdmaOne offered

some security predominantly by the sheer complexity of its

design. However, CDMA2000 offers complex scrambling to support priv'acy. The first phase ofCDMA2000 called CDMA2000

The transition from

G8M toWCDMA

requires a new

frequency

spectrum because

of the 5 MHz of

bandwidth that the

WCDMA waveform

requires. It cannot

fit into the smaller

spectrum space

currently allocated

to G8M.

CDMA2000 is one

of the most

important

proposals for an

IMT-2000 air

interface.

CDMA2000 is

formally

documented as 18-

2000 and builds on

its predecessor

CdmaOne (18-95).

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GENERAL I ARTICLE

Ix is an extension of the existing IS95B standard. It allows doubling of the system capacity and increased data rates up to 614 kbps. The second phase called CDMA2000 lxEV (Evolu­tion) is a further enhancement of CDMA2000 Ix. It includes High Data Rate (HDR) technology providing data rates up to

2.4 Mbps [3].

IS-2000 also supports smart antenna technology that signifi­cantly improves system capacity. Smart antennas can be steered electronically. This allows RF energy over a wide area that

dilutes the signal, causes interference and, ultimately, lowers

capacity. The path from CdmaOne to CDMA2000 will have minimal impact predominately due to the similarities of the two technologies.

Initially, a dedicated carrier is devoted to high-speed packet data, whereas one or more additional carriers are used to realize voice connections. In later developments of the lxEV, packet data and voice transmission will be combined in the carrier; however, packet services on a separate carrier may be possible. Finally, in the third phase of CDMA2000 development, called CDMA2000 3x, three independent non-overlapping CDMA channels are used, retaining backward compatibility with CDMA2000 Ix and IS-95B. Tripling the bandwidth and giving some additional freedom results in service enhancement and data rates up to 2 Mbps.

The CDMA2000 is designed to operate in the following envi­ronments:

Outdoor mega cells (cell radius> 35 km), Outdoor macro cells (cell radius I - 35 km), Indoor / outdoor microcells (cell radius < 1 km), Indoor / outdoor picocells (cell radius < 50 m), Wireless local loops.

2.3. CDMA 2000 lxEV-DO, IS-856 (3G)

lxEV-DO [5] is a data service technology that is formally speci-

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GENERAL I ARTICLE

fied as IS-856. EV signifies that it is an evolutionary technology built on the IS-95 standard.

What differentiates it from other 3G technologies is that it supports Data Only (DO). Voice services are not provided. By

optimizing the system for packet data, it is not limited by voice

timing requirements that are significantly different from data • requirements. lxEV-DO provides an always-on connection, which provides seamless Internet connectivity.

IS-856 can provide peak data rates of 2.4 Mbps in a 1.25 MHz IS-

95 COMA channel. It is also spectrally efficient. Given the cost

associated with a large frequency spectrum, the importance of this characteristic cannot be overstated. Simulations with fixed

and mobile users show that a spectral efficiency of 1 bit/sec/Hz is achievable. The high spectral efficiency is accomplished by a

combination of adaptive coding rate and adaptive modulation

technique~

3. Conclusion

Analog 1 G wireless cellular systems had many weaknesses, but

their importance cannot be overstated. They showed there was a huge worldwide market for mobile communication. Digital 2G

technology solved many of the weaknesses of 1 G, added services,

and saw the beginning oflow speed data communication. Present

cellular systems are based on TDMA and COMA technologies,

and provide packet data transmission at low rates. Advanced digital 3G technology represents a quantum leap in technology

from 2G. 3G mobile telecommunications systems pave the way

for future access to advanced multimedia services like mobile

Internet or videoconferencing.

Suggested Reading

[1] Azim Samjani, General

Packet Radio Service, IEEE

Potentials, ApriJlMay 2002.

[2] A Viterbi, CDMA: Princi­

ples of S,read Spectrum

Communication, Addison

Wesley Longman, 1995.

[3] T Rappaport, Wireless Com­

munications, Principles and

Practices, Prentice-Hall,

2nd Edition, 2002.

[4] H Honkasalo and others.,

WCDMAand WLAN for3G

and beyond, IEEE Wireless Communication Magazine,

Vol. 9, No.4, pp.14-18, April

2002.

[51 Richard Parry, CDMA2000

lxEV-DO a 3G wireless

Internet access system,

IEEE Potentials, pp.10-13,

October/November 2002.

Address for Correspondence

R Ramachandran

Department of Computer

Science and Engineering

Sri Venkateswora College of

Engineering

Sriperumbudur 602105, India.

Email: rrama@svce.ac.in

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